/*
 * @(#)$Id$$
 *
 * Copyright 2006-2008 Makoto YUI
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * 
 * Contributors:
 *     Google Inc.- initial implementation
 *     Makoto YUI - ported
 */
/**
 * Copyright (C) 2006 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package gridool.util.concurrent.reference;


import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * Starts a background thread that cleans up after reclaimed referents.
 *
 * @author Bob Lee (crazybob@google.com)
 * @author Makoto YUI (yuin405@gmail.com)
 */
class FinalizableReferenceQueue extends ReferenceQueue<Object> {

    private static final Logger logger = Logger.getLogger(FinalizableReferenceQueue.class.getName());

    private FinalizableReferenceQueue() {}

    void cleanUp(Reference reference) {
        try {
            ((FinalizableReference) reference).finalizeReferent();
        } catch (Throwable t) {
            deliverBadNews(t);
        }
    }

    void deliverBadNews(Throwable t) {
        logger.log(Level.SEVERE, "Error cleaning up after reference.", t);
    }

    void start() {
        Thread thread = new Thread("FinalizableReferenceQueue") {
            public void run() {
                while(true) {
                    try {
                        cleanUp(remove());
                    } catch (InterruptedException e) { /* ignore */
                    }
                }
            }
        };
        thread.setDaemon(true);
        thread.start();
    }

    static final ReferenceQueue<Object> instance = createAndStart();

    static FinalizableReferenceQueue createAndStart() {
        FinalizableReferenceQueue queue = new FinalizableReferenceQueue();
        queue.start();
        return queue;
    }

    /**
     * Gets instance.
     */
    public static ReferenceQueue<Object> getInstance() {
        return instance;
    }
}
